Deep breath ..... I'll probably be hung drawn and quartered by the end of this post but ....
.... whilst I agree that calling a child "evil" is far from ideal, I do totally understand why the OP flipped. It's awful to watch a younger child being bullied by an older one and in most cases there's a significant difference in size and strength between a 14 year old boy - a teenager and a 7 year old girl - a primary school child which makes any "normal" sibling "spatting" in this particular case a little bit different to bickering etc when the kids involved are much closer in age to each other. This particular incident was far from a one-off - it's been going on for 5 years IIRC .... and again, I find that especially nasty when you consider a 2 year old DD - a toddler, practically a baby really - being picked on by a much bigger child. My daughter's 9 and I would come down very hard indeed on her were she to be mean or to torment such a young child (or any child for that matter).
So - it's not surprising the OP lost it and all things considered I think SS deserved to have a strip torn off him. Yes - her choice of words was perhaps ill advised because the spoilt brat SS and his pathetic blinkered father have siezed upon the "terrible" thing she called him as opposed to the much worse behaviour and attitude that they both display towards DD. Comparing OP's outburst with SS's bullying and DH's blinkered ignorance/irresponsibility/favouritism I know which one I'd say was the lesser of two evils actually (no pun intended).
Okay .... you now have this stalemate situation and obviously splitting up would be a last resort and far from desirable. But on the other hand, if both SS and DH see nothing wrong in what they've done - for several bloody years - then how on earth is that going to benefit OP and her daughter. Poor kid - not only does she get picked on - but her dad never protects her. I find it very hard to believe that in 5 years he's never witnessed the bullying for himself - and if he has, then his head in the sand dishonesty about it is absolutely disgusting. Even if he's convinced himself he's not seen anything, why, does he always accept his son's word as read ? I remember arguing with my sister like most kids do but when either one of us went moaning to mum and dad if neither of them had seen what had happened they either ignored us both, or punished us both - they never favoured one of us over the other at all.
I don't think the OP should apologise as things stand. The current situation has all been turned around to be all about what she's done - which is far far less important than sorting out what they've done. For this family to be able to go forward, that needs to a) be acknowledged and b) be tackled .... which is going to be a huge ask as it's been going on for so long. Clearly, in order to keep ex and older child "sweet" dad has decided that he'll effectively sacrifice his younger child so he never has to challenge, discipline or heaven forbid punish his nasty brat of an older son. Presumably he's petrified about losing contact - such a familiar^ story - but that's simply not a good enough reason to betray his daughter the way he's been doing. I don't know if he'd be prepared to take that on board or not but yes, family counselling would be a very good idea as a last attempt to have him see sense. There's never any reason for perpetually favouring one child over another, and if he still refused to accept that after counselling, or, argued that he "had to" in order to "keep" SS then OP would have an answer once and for all about what he truly thought of her and their daughter. That is - if he agreed to speak to a 3rd party at all ... I think many of these men know damn well how monstrously unfair they're being but would refuse counselling because in a situation like this there really is only one right answer and that is to treat all your kids fairly. The ideal of course is that DH realises the error of his ways and agrees to impose fair discipline and boundaries with SS going forward in order to preserve his marriage and ensure his daughter is treated equally and fairly compared to SS.
OP - I feel so angry for you ..... yes, it's not unreasonable for your DH to feel desperately frightened about losing his son and he's in an unenviable position with a spiteful ex who has a history of alienating kids against their dad. For that, you have to feel sorry for him but good god, the right way of dealing with that is NOT to shit over your youngest child. What he should have done and believe me, I know first hand this is no easy answer either is to treat both kids the same (obviously age appropriateness notwithstanding) and if that included having to discipline SS every so often (show me a child who doesn't need to be disciplined ever!) then so be it. If the result of that meant loss of contact then DH should have immediately dragged the mother into court rather than rely upon her co-operation. And yes I also know court orders often aren't worth the paper they're written on but that's still the right thing to do when you have a bitter spiteful ex who won't back up the NRP over normal disciplinary issues. The men who choose the "easy" option of tiptoeing round their (invariably) spoilt and bratty kids who hold a totally inappropriate amount of power due to their parents being unable or refusing to co-operate pretty much disgust me whatever sympathy I feel for their fear of "losing" non resident kids .... you simply can't allow one child to take the hit (literally it would seem in this case) because you don't like the idea of the alternative - brat child stropping off. How bloody cowardly is that ?
So ..... OP, you've got this awful situation and in your shoes I'd tell your DH that you both need family counselling urgently to try and find a way forward. And personally speaking, I'd be happy to apologise for my poor choice of vocabulary but only when both DH and SS had offered genuine apologies of their own, together with a promise that things would be different from now on. At 14 SS is well old enough to know how he's behaving is wrong - I'm sure his school has an anti-bullying policy for example and I'm sure it's drummed into them. I wonder how his school would treat him if they found him bullying a Year 6 kid never mind a 7 year old. Yes, you can't say you're totally innocent in what's happened that'd be ridiculous but if you look at this as an overall and longstanding problem - which you should do - your contribution, oh dear, calling SS a nasty name under great provocation amounts to a tiny fraction of the larger issue. And that's why I think it's so important that DH and SS recognise how bloody awful they've been first. Not so you get the pleasure of "winning" or anything like that but because it's vital to the future of your family that they do so. If they can't/won't then I don't really see how you can carry on with DH - all your respect for him would have gone and just as importantly, your daughter's self esteem will be destroyed by not feeling her dad has her best interests at heart and that she's clearly second best.